The present application is a continuation of International Application No. PCT/SE2004/001926, filed Dec. 17, 2004, which claims priority to SE 0303446-9, filed Dec. 17, 2003, both of which are incorporated by reference.
The present invention relates to a process for use in a motor vehicle. The processes relate to an automatic gearshifting process with the vehicle in driving mode and a simultaneously engaged coupling-dependent power take off and automatic disengagement of said power take off with the vehicle in driving mode.
The power take off is disposed on the transmission of the vehicle.
In order rationally to be able to handle the load on a goods vehicle, load handling equipment is required. The most common examples of such equipment are tipper and crane. Other commonly found examples are load changer, garbage handling unit, rotary cement mixer, rinsing unit, refrigeration unit, pumping equipment for various types of liquids and air compressor for loading or unloading bulk loads.
In order to utilize the drive force of the vehicle engine to also drive the load-handling equipment, a power take off is required. The drive force from the power take off can either be transmitted mechanically via toothed gearings and shafts, chains or belts, or hydraulically by the fitting of a hydraulic pump on the power take off.
Power take offs are divided into coupling-independent and coupling-dependent power take offs. The coupling-dependent power take offs are mounted on the transmission and are usually driven by the intermediate shaft of the transmission. This means that the power take off is coupling-dependent, i.e., the power take off stops when the coupling between the engine and transmission of the vehicle is disconnected. Depending on whether the transmission is equipped with splitter gear or not, the gearing between the engine and the power take off can be affected.
Automatic transmissions of the automated step-geared transmissions type have become more and more common in heavy-duty vehicles as microcomputer technology has been increasingly developed and has made it possible, with a control computer and a number of controllers, for example servo motors, to precision-regulate engine speed, engagement and disengagement of an automated clutch between engine and transmission, as well as the internal coupling members of the transmission, in such a way and in such relation to one another that smooth gearshift is always obtained at the right speed.
The advantage with this type of automatic transmission compared with a traditional automatic transmission constructed with planetary gear steps and with a hydrodynamic torque converter on the input side is, firstly, that, particularly where there is a question of use in heavy-duty vehicles, it is simpler and more robust and can be produced at substantially lower cost than the traditional automatic transmission and, secondly, that it has higher efficiency, which means potentially lower fuel consumption.
According to the prior art, for the above-stated type of automated step-geared transmission, coupling-dependent power take offs are suitable for load-handling equipment which is used when the vehicle is stationary or is being driven only in start gear, for example tipper units, cranes, load changers, pumps for emptying/filling from various containers and air compressors for loading or unloading bulk loads.
U.S. Pat. No. 6,080,081 shows examples of a coupling-dependent power take off arrangement in a vehicle with automated step-geared transmission. The document deals with the engagement of the power take off.
It is general practice, in transmissions, to equip a gear with means for preventing unwanted disengagement in the transfer of torque at the gear. This in order to prevent accidental disengagement of the engaged gear.
Such means can be configured such that the coupling teeth, belonging to coupling sleeves forming part of the gear and to the disconnectable coupling rings of the gear wheels, are tapered such that mutually facing V-shaped ends of the teeth on the coupling sleeves and the coupling rings are wider than parts of the teeth remote from said ends. It is customary to say that the flanks of the coupling teeth are configured with “cutbacks”. An applied torque, for example the driving torque of the engine, on mutually contacting faces with cutbacks will produce a resultant force which acts in the direction of engagement of the coupling sleeve in order to stop an engaged gear from being accidentally disengaged. To enable an actuator disposed in the transmission to manage to disengage such a gear, torque applied to the gear must be reduced to the point where the actuator is able to disengage the gear. In order to minimize wear and possible damage, however, torquelessness is aimed for in the gear before it is disengaged. This can be effected, for example, by the transmission control unit, in a vehicle with an automatic step-geared transmission, ensuring that before the gear is disengaged the output torque of the engine is brought down to a minimum. Similar locking step to prevent accidental disengagement can also be found on coupling teeth in a claw clutch arranged to engage and disengage a coupling-dependent power take off in a vehicle. EP 1097018 shows examples of gear arrangements with cutbacks. As an alternative to cutbacks, the coupling teeth can be configured, for example, with more or less gradual variations in width, which width variations are meant to hook another when the engaging device is torque-loaded and thereby prevent accidental disengagement.
A problem with the prior art is that, in the case of an engaged coupling-dependent power take off, in which power is being tapped and in which a gear engaged in the transmission and equipped with means for preventing unwanted disengagement in the transfer of torque at the gear is simultaneously to be disengaged, the disengagement of the gear is unachievable, because of the said means.
Equivalent disengagement problems exist in power take offs in which the engaging/disengaging device of the power take off is constituted by a claw clutch with corresponding means for deterring accidental disengagement, i.e., through some form of coupling teeth with cutbacks. When a torque is applied to such power take offs through power tapping, a resultant force will therefore be generated, which acts in the direction of engagement of the claw clutch. According to the prior art, the vehicle needs to be stopped and the engine disconnected from the transmission in order to minimize the resultant force acting in the direction of engagement of the claw clutch and the power take off is thereby able to be disengaged.
Another problem with gearshifting with engaged coupling-dependent power take off is that the power tapping of the power take off affects the synchronization process. When so-called non-synchronized gears are engaged in automated step-geared transmissions, this problem can be circumvented by advanced controlling of the engine speed. In the case of engagement of so-called synchronized gears, the torque of the power take off will place load upon the synchronization, which produces increased wear and, for relatively large torque tappings, might also make synchronization impossible.
According to the prior art, the only way to ensure that the power take off does not load the transmission with any torque is by seeing to it that the power take off does not rotate. The driver of a vehicle with coupling-dependent power take off is therefore confined to using the coupling-dependent power take off when the vehicle is stationary or if a start gear is engaged, that the vehicle can be driven only in this gear whilst the power take off is engaged. Added to this are the difficulties in disengaging the power take off under load according to the above. In the case of gears and claw clutches without means for deterring accidental disengagement, comfort problems can also arise if the gear and/or the claw clutch are disengaged under torque load. These restrictions preclude the use of transmission-mounted coupling-dependent power take offs in a number of applications, including refrigeration/freezing transportations and driving rotary cement mixers.
There is therefore a need, in a vehicle equipped with power-dependent power take off and step-geared transmission, to be able to use the coupling-dependent power take off of the vehicle when the vehicle is in motion and with the facility to shift satisfactorily between all the gears of the vehicle over the full speed register of the vehicle and with the facility to disengage the power take off satisfactorily at any time during travel.
The first process according to the invention describes an automatic gearshifting process for a vehicle with engaged coupling-dependent power take off when the vehicle is in motion. The power take off is driven by an engine disposed in the vehicle via at least one clutch, which, in turn, is coupled to an automatic step-geared transmission in which there is disposed at least one intermediate shaft, used to drive the power take off. The transmission, the engine and the power take off are controlled by at least one control unit.
The gearshifting process is characterized in that the control unit limits the power tapping at the power take off during at least a part of the gearshifting process when the intermediate shaft is disconnected from the drive wheels of the vehicle with a view to limiting the torque load of the power take off across said transmission.
The limitation of the power tapping at the power take off lessens the torque load over the engaging/disengaging device of the transmission and thereby reduces the force required to disconnect the engaging/disengaging device, so that the transmission can be brought to a neutral position in which the power take off is disconnected from the output shaft of the transmission without comfort problems and without wear to the engagement/disengagement mechanism in the transmission. With the invention, it is therefore possible to shift gear when the vehicle is in motion, even when a coupling-dependent power take off is engaged and the starting position is that power is being tapped from the power take off. The facility to shift gear whilst the coupling-dependent power take off is engaged and the vehicle is in motion increases the number of possible types of auxiliary units which can be installed in the vehicle.
The second process according to the invention describes an automatic disengagement process of a coupling-dependent power take off in a vehicle when the vehicle is in motion. The power take off is driven by an engine disposed in the vehicle via a clutch, which, in turn, is coupled to an automatic step-geared transmission which drives the power take off. The transmission, the engine and the power take off are controlled by at least one control unit. The disengagement process comprises the steps: control unit limits the power tapping at the power take off, control unit disengages the power take off.
The advantage with the second process according to the invention is that the limitation of the power tapping from the power take off by the control unit lessens the applied torque and hence reduces the force required to disconnect the engaging/disengaging device of the power take off. The second process according to the invention therefore enables the control unit better to disengage the power take off when the vehicle is in motion, even when a coupling-dependent power take off is engaged and the starting position is that power is being tapped from the power take off.
According to one embodiment of the invention, the disengagement process comprises the steps: control unit limits the power tapping at the power take off; control unit disconnects the engine from the transmission; —the control unit puts the transmission into neutral position so that the power take off is disconnected from the drive wheels of the vehicle; control unit disengages the power take off.
The advantage with this embodiment is that the disconnection of the power take off both from the engine and from the drive wheels by the control unit ensures that only a very small torque loads the engaging device of the power take off as it is disconnected. The disconnection from the drive wheels can be realized by the power take off being disconnected from a main shaft disposed in the transmission or by a range gear disposed in the transmission being put into neutral position.
In a preferred embodiment based on any one of the above-stated processes, the control unit brings down the power tapping at the power take off to a minimum, i.e., zero power tapping or almost zero power tapping.
This ensures that the gear can be disengaged so that the transmission can assume neutral position and the control unit can engage a new gear and that the claw clutch can be disengaged. This produces increased comfort in the vehicle. A further advantage is that wear in the claw clutch and in the gear concerned is reduced.
In a further preferred embodiment based on any one of the above-stated processes, the gear and the claw clutch are respectively equipped with means for deterring accidental disengagement, i.e., coupling teeth with cutbacks, for example. The fact that, according to the invention, the control unit limits the power tapping from the power take off serves to reduce the applied torque and hence minimize the force required to disconnect the engaging/disengaging device of the gear and of the power take off respectively. It thereby becomes possible to shift gear or disengage the power take off even when the vehicle is in motion and despite the starting position being that power is being tapped from the power take off. It is therefore possible, with the aid of the processes according to the invention, to drive all types of unit by the coupling-dependent power take off in all gears, both forward and reverse, over the full speed register of the vehicle, irrespective of whether the vehicle is stationary or in motion. This also includes units which, according to the prior art, are required to be driven by a coupling-dependent power take off. Various configurations of units which are to be driven with power take off will hereby be easier to install in the vehicle.